AN EXTRA DYAD AND EXTRA TETRAD IN CAMNULA Od 
The material on which this report is based consists of the 
testes of ten individuals from certain islands in Puget Sound. 
Individuals 950, 951, 954.1, and 980 were collected by Doctor 
McClung in 1909. The remainder, 2482, 2508, 2511, 2518, 
2525, and 2526, were secured by Doctor Carothers during the 
summer of 1915. 
In addition to these animals, there is a considerable amount 
of material in Doctor McClung’s collection from the Puget 
Sound region and from various other sections of the United 
States and Canada. I have gone over much of this material, 
making random counts in the customary manner, without dis- 
covering anything unusual in chromosome number or behavior. 
But a detailed study was made of only the ten individuals men- 
tioned above, and we are concerned here chiefly with the peculiar 
conditions, seemingly unique among cytological phenomena, 
found in five of these ten animals.! 
I am indebted to Dr. C. KE. McClung and Dr. E. Eleanor 
Carothers, of the University of Pennsylvania, for the use of the 
material, for much valuable instruction in cytological methods, 
and for giving so generously of their time in checking up many 
of my observations. It is only fair to them to state, however, 
that the nature of the phenomena described and the amount of 
statistical matter presented in this paper are such that mistakes 
or imperfections in the work might easily escape detection by 
even such able cytologists. 
Dr. P. P. Calvert, of the University of Pennsylvania, and Mr. 
J. A. G. Rehn, of the Academy of Natural Sciences of Philadel- 
phia, have kindly furnished me with information concerning the 
taxonomy and distribution of Camnula pellucida. Mr. Rehn 
confirmed the identification of nine of the ten animals used in 
this investigation. (The tenth specimen, 950, was lost.) 
Miss Ruth McClung was good enough to prepare for me some 
transverse sections of a camnulan testis with which to check my 
counts of the follicles. 
1 Some years ago Doctor McClung, in a preliminary survey of a number of 
species, noticed some peculiarity about the complexes of specimen 950; but 
when the present study was begun it was not suspected that variations in the 
chromosome number occurred within the individual. 
